Hydrocarbon conversion



May 5, 1959 L. P. EVANS HYDROCARBON CONVERSION Filed Oct. 15, 1954 1NVENTOR SEAL 6 H ATTORNEY Unite. f States atet HYDROCARBON CONVERSIONLouis P. Evans, Woodbury, N..l., assignor to Socony Mobil Oil Company,Inc., a corporation of New Yorlr Application October 13, 1954, SerialNo. 461,965

2 Claims. (Cl. 214-152) This invention relates to hydrocarbon conversionsystems and more particularly to the maintenance in such systems ofseals between zones of different pressures.

In the cracking of hydrocarbons to produce an increased yield ofhydrocarbons boiling in the gasoline range it is customary to employ acontinuously moving bed of granular catalyst material. Succeedingportions of this material fiow through a reactor in which the conversionof the hydrocarbon material takes place. During this reaction thecontact material becomes contaminated and provision is therefore made todeliver the moving bed to a regenerator wherein the contaminants areburned off. Succeeding portions of the regenerated contact material arethen returned to the reaction or conversion zone.

It is desirable that the hydrocarbon conversion take place underpressure and that the regeneration of the contact material take place atatmospheric pressure. Accordingly the problem is presented ofcontinuously feeding contact material into a regeneration zone whilemaintaining a positive pressure above atmospheric within that zone. Oneway to eifect the seal is to use valves. These are, however,discontinuous in operation, expensive to install and maintain, anddamaging to the contact material. Accordingly, resort has been had tofeed legs long enough to maintain a head of contact material sufiicientto keep the desired pressure level within the reactor. Since there issometimes a considerable variation in the pressure within the reactor avalve has been retained for use under emergency conditions. While thisarrangement involves only emergency use of a valve, it has been foundthat the valve is inclined to fail at the very time it is most needed.

It is, therefore, an object of the present invention to overcome thedisadvantages of the prior art and to provide for the safe sealing ofhigh pressures without the use of a mechanical safety valve by providinga pressure release and alarm system.

It is contemplated according to the present invention to prevent, by anautomatic pressure adjustment, stoppage or reversal of contact materialflow in a feed leg to a reactor when the pressure in the reactortemporarily exceeds the head of contact material.

Other objects and advantages of this invention will be apparent uponconsideration of the following detailed description of a preferredembodiment thereof in conjunction with the annexed drawings, the singlefigure of which shows a portion of a moving bed contact material systemwith the present invention in operative position.

Referring now to the drawing in greater detail, it can be seen that theillustrated part of the system comprises an upper feed hopper It a sealleg 11, a lower feed hopper or intermediate pressure pot 12, a shortfeed leg 13, and a reactor 14. The moving bed of catalyst materialenters the illustrated part of the system through a conduit which is fedby a contact material elevator or the like. hopper 10, where the movingbed is established. The moving bed of material gravitates through theseal leg The contact material flows into the feed 11 and through the top16 of the pressure pot 12. If there discharges into the pressure pot 12,from which it gravitates through the short leg 13 into the top of thereactor 14. A line 17 delivers a seal gas such as steam or flue gas tothe top of the reactor 14.

In accordance with conventional practice, the contact material isdischarged from the elevator through the conduit 15 into the feed hopper10 at substantially atmospheric pressure. The catalyst gravitates as acompact mass'through the elongated feed leg 11 into the top of thereactor 14, the reactor pressure being about 10 pounds per square inchgauge. In normal operation this feeding is continuous. A seal gas, suchas steam or flue gas, is introduced through the conduit 17 into the topsection of the reactor 14 at a pressure just slightly higher than thereactor pressure, such as, for example, 10% to 10 /2 pounds, therebyproducing a slight flow of gas upwardly through the seal leg to preventreaction materials from flowing up through the seal leg. Thus, themoving bed of granular contact material extending from the feed hopper10 to the reactor 14 itself constitutes the seal which prevents loss ofpressure from the vessel 14. The height of the column of contactmaterial above the reactor 14- is chosen in such a way that the weightper unit area of the bottom of the column of Contact material is greaterthan the pressure per unit area existing within the reactor. Under theseconditions gravity flow of the granular contact material continues andthe reactor is maintained sealed.

Occasionally, because of processing difiiculties, the pressure withinthe reactor 14 exceeds the design pressure for the system. It used to becustomary .to provide a cut-off valve near the bottom of the seal legsuch as the leg 11. This was an emergency valve and it was intended toisolate the seal leg from the reactor if the reactor pressure got abovea safe value. The valve did not operate very often and when called uponto operate failed on enough occasions to render its eliminationdesirable. According to this invention a valveless feeder technique isprovided to provide a measure of safety in the event that the reactorpressure gets too high. The pressure pot 12 is a part of the apparatusintroduced to eliminate a valve near the bottom of the leg 11. Alsoconstituting a part of this system is a conduit 18 leading from the topof the pressure pct 12 to a dilferential pressure measurement device 19.Another conduit Ztl leads from the device 19 to the top of the seal leg11. The diiferential pressure device 19 is not described in detail butit is understood that it may be of any of the well known devicesavailable on the market today which are capable of closing an electriccircuit in response to a pressure difference in excess of apredetermined value. The electric circuit may be connected to an alarmdevice and/or to a valve such as valve 21 which is connected through aconduit 22 to the gas zone at the top of the pot 12. A major portion ofthe seal leg 11 is above the seal pot 12 and discharges catalyst intothe seal pot. Normally, the vent valve 21 is closed so that the catalystfeeds uniformly into the reactor. When the pressure in the reactor risesabove a safe level, the event 21 opens, permitting seal gas to escapefrom the region in the seal pot 12 above the bed of catalyst. Thisprovides a pressure differential across the short leg 13 more thansutficient to elevate the catalyst in the leg. However, the vessel 12has a substantially greater cross-section than the seal leg 13 so thatthe gas flowing upwardly through the catalyst is dispersed in the massand the upward velocity of the gas is reduced below what is termed thebed disrupting velocity. The bed disrupting velocity is that upwardvelocity at which the catalyst just starts to be disturbed or go intoboiling movement with increase in gas velocity.

Patented May 5, 1959- The catalyst mass in hopper 12 has a cross-sectionlarge enough to reduce the gas velocity below the bed disruptingvelocity at some level below the surface of the catalyst mass. There is,therefore, provided above this critical level a sufiicient depth ofcatalyst to provide a downward force component which will keep thecontact material in the conduit 13 in compact and static condition.This, of course, prevents the transfer of catalyst through the seal leg11 and the catalyst level will commence to rise in the feed hopper 10and the unit must be shut down or the difiiculty corrected promptly inorder to prevent catalyst from flowing back from conduit 15 into therising elevator or pneumatic lift. It is seen that during theseemergency conditions no catalyst will flow through the seal leg andthrough the conduit 13, but catalyst may be drawn downwardly through thereactor and away from the lower end of pipe 13, leaving the catalystsuspended in the legs 11 and 13 until such time as normal conditions arerestored.

This entire operation is automatic. The dual pressure indicator 19measures the pressure differential across the seal leg during normaloperation and when thispressure difierential exceeds a safe upper limitit actuates the valve 21, thereby positively preventing the flow ofcatalyst through the seal leg system until the difliculties arecorrected. Since the dual pressure indicator is also connected to analarm, the operator is. warned to either correct the difliculty andresume normal operation or shut the unit down promptly to preventoperational difliculties.

The leg 13 does not have to be very long but at least some length of legmust be provided. It should be at least 2% times the diameter in length,and preferably as much as times the diameter in length.

What is claimed is:

1. In a process in which a granular contact material is transferred as acompact gravitating column through reaction and regeneration zones,wherein the reaction zone pressure is substantially greater than theregeneration zone pressure and wherein the granular material isintroduced into the higher pressure reaction zone as a 4 compactgravitating column of restricted cross-section and elongated heightlocated directly above the reaction zone from a storage zone atop thecolumn maintained at substantially the same pressure as the regenerationzone, the method of providing a safety seal to prevent the escape ofreactants from the reaction zone and loss of the compact gravitatingseal column in the event of the occurrence of abnormally high pressurein the reaction zone comprising the steps of: introducing a seal gasinto the elongated column at the lower end thereof at a pressure notsubstantially greater than the reaction zone pressure, expanding thecolumn laterally in the lower portion of a safety zone locatedintermediate the top and bottom of the column, so that as the contactmaterial gravitates in compact form through the safety zone it covers across-sectional area substantially greater than the cross-section of thecolumn above and below the safety zone, withdrawing gas from the upperportion of the safety zone in response to a rise of pressure in thereaction zone above a determined safe operating pressure at a flow ratesufficient to substantially reduce the upward gas velocity of gasflowing upwardly through the column in the safety zone to a gas velocitybelow the bed disruption velocity, the cross-section and depth of thecolumn in the safety zone being sulficient to maintain the column incompact static condition whereby the escape of reactants from thereaction zone is prevented and the compact column is retained intactuntil normal operating conditions are restored in the reaction zone.

2. Claim 1 further characterized in that a warning alarm isautomatically sounded simultaneously with the stoppage of flow of thecolumn of contact material.

References Cited in the file of this patent UNITED STATES PATENTS2,441,311 Crowley et al. May 11, 1948 2,448,272 Payne et a1. Aug. 31,1948 2,488,488 Bergstrorn Nov. 15, 1949 2,626,235 Wilson Jan. 20, 19532,709,674 Bergstrom May 31, 1955

